The standard piston engine wastes an enormous amount of energy by reversing direction of reciprocating parts such as pistons, valves, and tappets. As a result this type of engine generates considerable vibration and operates with a low degree of efficiency.
The rotary Wankel engine operates somewhat more smoothly. Nonetheless the rotor of this machine follows a noncircular path and therefore the engine develops a certain amount of throw. In addition complex seals that must move over noncircular paths are prone to leakage, and as a result the operating efficiency is less than ideal.
The standard jet-type turbine engine which converts the axial thrust of a continuous combustion into rotation is normally usable only in stationary applications. These engines are relatively dangerous and cannot find application in a standard motor vehicle.
Even if the combustion is contained such a turbine engine has no braking effect, like a piston engine. If the gas is released while a turbine-equipped car is going downhill, the engine will offer no appreciable resistance to being reverse-driven. This further makes such engines only limitedly usable in motor vehicles.